The overall objective of this proposal is to use the current understanding of host defenses against schistosomiasis and of the biochemistry and molecular biology of the causative organisms to develop immunologic alternatives to control. Such an effort is needed because of the global prevalence of infection and the burden of illness in human population infected with several species of schistosomes. In spite of the recently developed anti-schistosome drugs, their long term effect and the danger of drug resistance may become a limiting factor in their usefulness as control measures. The target organism is a formidable immunologic challenge but recent evidence from our laboratory and others indicate that monoclonal antibodies and purified parasite antigens are capable of inducing significant resistance in experimental animals. Furthermore, the expanding science and technology of vaccine development and delivery offer new unique opportunities. We therefore propose to use the knowledge of host protective responses, its mechanisms and the increasingly expanding molecular understanding of schistosomes in order to isolate and characterize parasite antigens that can be tested as candidate vaccines. The specific aims of this proposal are: 1. Biochemical characterization and cloning of protective antigens. 2. Selection of candidate subunit peptides for vaccines development. 3. Determination of optimal vaccination strategies. 4. Evaluation of human response to candidate vaccines. The proposal is designed as a series of step by step studies by using first immunoaffinity and biochemical procedures to purify two candidate antigens (SmW68 and SmW43) that have been identified by protective monoclonal antibodies. This will be followed by HPLC repurification using reverse phase hydrophobic interaction or ion exchange columns. Components peptides for amino acid sequence analysis will be generated from deglycosylate antigens by limited tryptic digestion. The larger peptides with single N- terminal will then be sequenced. Isolation of corresponding cDNAs from expression libraries will be achieved either by immunologic screening or by using oligonucleotide probes. Once defined peptide sequence are identified, we will use a combination of immunologic and biochemical procedures to delineate immunogenic epitopes and their effectiveness in inducing resistance in mice to be challenged percutaneously with S. mansoni. A major goal is to test these candidate vaccines for lack of sensitization to the immunopathological sequelae of schistosomiasis. Optimal vaccination strategies with stimulation of specific components of the host immune response or with clinically acceptable adjuvants will be determined. In addition, sera and peripheral mononuclear cells from individuals infected with S. mansoni will be examined for antibodies and sensitized T cells to candidate vaccine individuals infected with S. mansoni will be examined for antibodies and sensitized T cells to candidate vaccine antigens. We will also examine the in vivo human response to vaccination using the SCID-hu mouse model. Results obtained from these studies should pave the way to defining candidates for anti-schistosome vaccine.